Along with the advancement of semiconductor processing technology, it has become difficult to achieve desired characteristics by means of the known two-dimensional scaling method. Furthermore, along with reduction in feature size, problems regarding the short-channel effects and the like have begun surfacing. Therefore, there has been a need for a breakthrough other than a simple reduction in feature size.
Semiconductor nanowires have been receiving attention because of the possibility of obtaining transistors having a good electrical characteristic, and the like. Examples of nanowire fabrication techniques include a top-down method in which lithography and etching are used and a bottom-up method typified by a vapor-liquid-solid (VLS) method. By using the bottom-up method, for example, it is possible to obtain nanowires composed of a single-crystal semiconductor which have a circular cross section with a diameter of 500 nm or less and which have a low crystal defect density. However, this method has not been put into practical use because of difficulties in control of growth orientation and position.
There is a known method in which grown nanowires are separated from a substrate by a stimulus, such as ultrasonic waves, in a solution, collected, and then applied and arranged horizontally on another substrate, followed by formation of electrodes on both ends. In this method, nanowires are laid out randomly on the surface of the substrate, and therefore, it is difficult to fabricate a device with high reproducibility of characteristics. Furthermore, since a complex process is required, mass production is difficult.
In contrast, PTL 1 discloses a method in which nanowires VLS-grown perpendicular to a substrate are, without using a step of relocation to another substrate, directly fabricated into a device on the substrate on which the nanowires have been grown.